Galaxies and the Milky Way

What is a galaxy?

Galaxy, it is the name of our galaxy, it is an enormous spiral wheel of stars, a diameter of 100 000 light years. What appears of the Earth, it is a white continuous band of the Milky Way. This galaxy really consists of three spiral arms (The arm Sagittarius, the arm of Orion and the arm Perseus). The mass of our Galaxy is of 2x1041 kg or 1011 solar masses. Numerous indications suggest that the center of numerous galaxies is occupied by a black hole. A galaxy is thus an assembly of stars, interstellar matter and probably big quantities of dark matter, the cohesion of which is assured by the strengths of gravitation, and the mass of which is of an order of height superior to hundred million solar masses. The Big and the Small Cloud of Magellan are nearby galaxies of ours, visible in the southern latitudes. They are with the Milky Way and Andromeda, the only visible galaxies in the bare eye. The Galaxies interact with their neighbors, and these interactions modify their shape. Two galaxies can even merge. The galaxies are three main morphological types: elliptic, spiral, irregular. As stars, which are grouped together in galaxies, most of the galaxies are also bound between them by the strength of gravitation. A structure containing until about fifty galaxies is a group of galaxies.

A structure containing several thousand galaxies grouped in a sector of some mega parsecs is a heap of galaxies. The groups and the heap of galaxies are grouped together in super heap, huge collections themselves containing tens of thousand galaxies. On a very large scale, the distribution of the heap of galaxies is not uniform, but not organized in patches or in strands.The spatial telescope Hubble sends regularly images showing us all the variety of the galaxies.

Image: Our Galaxy is of type spiral quite as the galaxy M83 above. Spiral galaxies are the most prevalent, they look like cosmic hurricanes.

Large spiral galaxies

The Sun is located in the Orion Arm of our Galaxy and rotates at a speed of 254 km/s around the galactic center, completing one revolution every 250 million years. A large spiral galaxy like ours, can be seen with the naked eye. Located in the constellation Andromeda, the Great Nebula in Andromeda (M31) is identical to ours, it is located 2.3 million light-years. Together, these galaxies dominate the mass of the local group. One can only marvel at the beauty of these bricks of the universe. The galaxies are hundreds of billions, and their number increases every time our space technology is perfected, pushing the year. Galaxies are born, 3 to 4 billion years after the Big Bang. It is gravity that has transformed diffuse clouds of hydrogen and helium, into embryos of galaxies. These embryos have collapsed as a result of their own gravity. This collapse was compressed and heated gaseous matter, turning it into hundreds of billions of soft balls, a few million degrees, called "stars."

When all the gaseous matter has been transformed into stars, these galaxies become elliptical, 30% of galaxies are elliptical. Some galaxies are able to turn into stars, 80% of the gaseous mass, the remaining fifth is flattened into a thin disk, continuing to turn into stars, much more slowly and preferably along the spiral arms which are developing. These are the spiral galaxies that dominate the galactic world, 60% of galaxies are spirals. They are found mainly in peripheral regions of galaxy clusters. Other galaxies are much more time to convert the gaseous matter into stars, because they are dwarfs, they contain only a few billion stars, having no special form, they are called irregular galaxies. 10% of galaxies are irregular.

Image: Type spiral galaxy seen edge. This image shows the disk of the galaxy NGC 4565.

Density of galaxies

Galaxies live among other galaxies and interact with their environment, especially where the density of galaxies is very high, the heart of the cluster can be found 1000 to 10 000 galaxies in a cube of a few million light years aside. In our local group, there are only 10 galaxies in a cube of equal size. The galaxies in the cluster move at a speed of about 1000 km/s. In such a traffic collision risks are quite high (one every 100 million to 1 billion years). These collisions can only be clashes, where the scratches are limited to a loss of outer stars, torn from their galaxy, they then form a sea of intergalactic stars. This pile, a billion years later take the form of an elliptical galaxy. Occasionally, the collision takes place with full force, galaxies merge and the new more massive galaxy gets brighter, as in the image against.

If the collision between two spiral galaxies, the disk of one of them can be piercing, becoming a ring-shaped galaxy. This hole will not last, the stars of the border will eventually fill it in less than a billion years and become an elliptical galaxy. There are some giant elliptical galaxies in the heart of the cluster, they are 10 times larger and brighter than their neighbors. Their mass exerts a gravitational force so that the galaxies passing close are swallowed. The giant galaxy becomes even more massive and more attractive. A giant galaxy swallows a galaxy every billion years.

Center of the Milky Way

The Milky Way is the central region of our galaxy. On the infrared image against this we see the exact center of our galaxy, known as the Central Molecular Zone and purple, the arch radio galactic center. A number of emission nebulae are visible through the massive young stars that illuminate from within. Like nearly all galaxies, our home galaxy at its center, a black hole. This black hole is called Sgr A. The galactic center is also home to the region of star formation, the most active of the galaxy.

* This image, in addition to its scientific interest, won the first prize of the photographic UAI / NRAO of 2008. Credit: A. Ginsburg (U. Colorado - Boulder), and al. BGPS team, team GLIMPSE II.

Small cloud of Magellan

This irregular galaxy which seems to orbit around the Milky Way is since observed time prehistoric by the inhabitants of the southern hemisphere, but it is the route around Ferdinand Magellan's world which will give his name. The Portuguese sailor Ferdinand Magellan and his equipage had all the time to study the southern sky during their navigation around the planet, at the beginning of the 16th century. These cosmic clouds are really irregular dwarfish galaxies, satellites of our own Galaxy. The Small Cloud of Magellan, Cover 15 000 light years in its biggest extension and contains several hundreds of million stars.

Situated in about 210 000 light years of us in the constellation of the Toucan. It is a part of the most close galaxies, the Milky Way, with the dwarfish galaxies of the Big Dog (approximately 25 000 light years), of the Sagittarius (approximately 3,5 million light years) and of the Big Cloud of Magellan (approximately 179 000 light years). With a visible magnitude of 2,7, it is also one of the most remote objects which can be seen in the bare eye. With a declension about 72 °, it is visible easily only since the southern hemisphere. It forms a couple with the Big Cloud of Magellan, situated 20 ° more in the East. As he, it is apparently an former blocked spiral galaxy which was deformed by the strengths of tide of the Milky Way. The Small Cloud of Magellan is a member of the local Group, our galactic heap.The Small Cloud of Magellan is connected with the Big Cloud by a bridge of gas and stars. These two clouds undergo the strengths of tide of the Milky Way.

Image: Magnificent sight of the small cloud of Magellan (credit NASA)

Image: This sight of the small cloud of Magellan, includes also two heap spherical leading, NGC 362, the luminous point at the bottom of the image and 47 Toucan to the left of the Small Cloud of Magellan. The heap 47 Toucan is hardly 13 000 light years of us.

Spiral galaxy M33 or NGC 598

The galaxy of the Triangle, also known under the name of M33, is a spiral galaxy of type Sc, situated in the constellation of the Triangle. The galaxy M33 NGC 598 the third of the local Group in ascending order, after the Milky Way and Andromeda. This galaxy is small compared with its neighbor, the galaxy of Andromeda M31, and with our Milky Way, but in the average of the spiral galaxies of the universe. M33 approaches us in 182 km/sec according to R. Brent Tully, or in 179 +/-3 km/sec according to the Ned. It is situated in 3 million years light. This galaxy was probably discovered before 1654 by Hodierna, follower of Galilee, who maybe grouped it with the opened heap NGC 752.

It was independently rediscovered on August 25th, 1764 by Charles Messier who cataloged it as M33. Classified by William Herschel September 11th, 1784 under the name H V.17, the galaxy of the Triangle was one of the first spiral nebulas identified as some by William Parsons.

Image: The galaxy M33 ou NGC 598, the third galaxy of the Local Group.

Spiral galaxy NGC1232

The galaxy NGC 1232 is in the constellation Eridanus (the river). Distant about 100 million light years. At this distance, the size of the image corresponds to approximately 200 000 light years, is twice the size of our Milky Way. We can notice below to the left, the small galaxy was deformed by the enormous galaxy NGC on 1232.

Image: We notice the difference of color enter the reddish nucleus (old stars) and the arms populated with young stars, thus blue stars. To note the small galaxy companion below to the left.

credit photo: European Southern Observatory ESO/VLT

Spiral galaxy M104 or NGC 4594

Galaxy of the Sombrero M 104 NGC 4594 in the heap Virgo. This brilliant galaxy owes this name of Sombrero to its appearance. According De Vaucouleurs, we see it since just 6 degrees in the South of the equatorial plan, realized by a thick dark band of opaque dust. This characteristic was probably the William Herschel's first discovery with its big telescope.

Image: Opposite, the dissimilar image of 3 photos taken by the camera FORS1 of the VLT Antu (European telescope of 8,2 m of the ESO based in Chile). It was obtained after an exposure of 6:20 am on January 30th, 2000.

Spiral galaxy M101 or NGC 5457

Galaxy " Pinwheel " M101 or NGC 5457, called also the Galaxy of the Mill, is a spiral galaxy among the most brilliant of the sky. M101 belongs to a group of at least 9 galaxies, the most striking members of which are NGC 5474 and NGC 5585. Other likely members of the group NGC 5204, NGC 5238, NGC 5477, UGC 8508, UGC 8837, and UGC 9405. The distance of M101: 24 (+/-2) million light years. With a diameter of 170 000 light years it is situated among the biggest galaxies. M 101, is a striking example of spiral galaxy, the relative nearness of which about 22 million light years allows to study it in detail. It seems that gravitational interactions with a nearby galaxy create waves of high mass and condense the gas which continues to turn around the center of the galaxy. These waves compress the incited gas and provoke the formation of stars.

The result is that M 101, has numerous regions of formation of extremely brilliant stars (called regions HII) spread over the spiral arms. M 101 is so big as its immense gravity deforms the smallest close galaxies.

Spiral galaxy M81 or NGC 3031 et M82

The buxom and beautiful spiral galaxy M81 lies in the constellation Ursa Major. It was discovered by Johann Elert Bode in 1774. M81 NGC 3031, is a spectacular galaxy, easily detectable with binoculars. This galaxy forms a pair with remarkable M82, a member of the group called M81 group. The two galaxies are close enough because the distance between their centers is only about 150 000 light years. This is one of the brightest galaxies in the heavens land, M 81 is also home to the second brightest supernova. The view below cons, reveals a bright yellow nucleus, blue spiral arms and large streaks of dust, all characteristics quite similar to the Milky Way. A trail of dust especially remarkable, pierces the galactic disk, below, left and right kernel.

This vein of dust may be wandering the trace of a persistent rustling between M81 and its smaller satellite galaxy, M82. An examination of variable stars in M81 has yielded a distance determinations of the most reliable external galaxy, with 11.8 million light years.

Image: Ci-cons, the galaxies M81 and M82 right to left. These two giant galaxies deliver an intense gravitational battle that has lasted for billions of years. The severity of each galaxy in a major way affects the other. Credit & Copyright: Leonardo Orazi

Spiral galaxy M74

With a striking nucleus and spiral arms developed possessions, M74 is a spiral galaxy, distant from 30 million light years, seen by the top situated in the Whale. It was discovered by Pierre Méchain in 1780 then observed by Charles Messier who integrated it into the catalog, some weeks later.Its mass is only 1/5 of that of our Galaxy but its diameter is 80 000 light years. The spiral arms contain many young stars or still in formation.

M74 is the most brilliant constituent of a heap of galaxies which includes besides: NGC 660, UGC on 1171, UGC on 1175, UGC on 1176, UGC on 1195 and UGC on 1200.

Galaxy NGC1672

Numerous spiral galaxies present a bar in their center, but it certainly has nothing to do with prominent bar of the spiral galaxy NGC on visible 1672 opposite. We distinguish, veins of dusts represented by dark strands, of young people heap of blue stars, nebulas to the characteristic red brightness of the hydrogen, the long and brilliant one bar of stars there overlapping in the center, and to finish a brilliant active nucleus which accommodates probably a super massive black hole. The light puts not less than 60 million years to reach us from NGC on 1672, which measures about 75 000 light years of diameter. NGC 1672 is visible in the constellation of the Sea bream and makes the object of studies to discover how the bar can contribute to the formation of stars in the central regions of the galaxy.NGC 1672 shows here its region of formation of stars which is in a central galactic bar.

Arms in spiral do not twist themselves completely since the center as we are in the habit of seeing it on the spiral galaxies but are attached to both ends of a straight bar of stars including the nucleus. The question which settles is: they develop systematically in the center of the spiral galaxies to disappear then. The visible galaxies behind NGC 1672 give the illusion to be incorporated into the leading galaxy, while they are much more taken away.

Image: This remarkable image supplies a sight high definition of the big bar of the galaxy NGC on visible 1672 in the southern hemisphere, in the constellation of the Sea bream. Credit NASA: image of the spatial telescope Hubble

Galaxy Cartwheel or ESO 350-40

The Galaxy of the wheel of the cart (so known under the name of ESO 350-40) is a lenticular or annular galaxy situated in approximately 500 million years light of distance in the constellation of the sculptor in the southern hemisphere. It is surrounded with a ring of 150 000 light years of diameter, consisted of young and brilliant stars.This galaxy was a galaxy identical to the Milky Way before it undergoes a head-on collision with a nearby galaxy. When the nearby galaxy crossed the Galaxy Cartwheel, the strength of the collision caused a powerful shock wave on the galaxy, as a stone thrown in one has a good laugh. By moving at high speed, this shock wave swept the gas and the dust, so creating a halo around the central part of the galaxy remained unhurt. It explains the bluish cloud around the center, the more brilliant part.

Image: Galaxy CartWheel seen by the telescope Hubble.

Spiral galaxy NGC2683

NGC 2683 is a spiral galaxy of magnitude 10, situated on the border of the Cancer. NGC2683 is situated between the constellation of the Lynx and that of the Cancer. Its peculiarity is that it appears at us of profile. Indeed, it is almost completely tilted, it does not allow us to distinguish the spiral arms and the central bulb of the galaxy. The fact of seeing the galaxy by the slice allows easily to measure the curve of rotation of the galaxy by using the Doppler effect. By estimating the rotation speed according to the distance in the center of the galaxy, we can determine the mass of the galaxy, it is this technique which shows the presence of dark matter in the Universe.

Image: both galaxies NGC4038 and 4039 began to collide.

Galaxy NGC4465, heavenly masterpiece

The galaxy NGC 4565 is a beautiful spiral galaxy, similar to ours. The beautiful spiral galaxy NGC 4565 is seen from Earth. Also known as the Needle Galaxy for its narrow profile. The brilliant NGC 4565 is a show for spring telescopes of the northern hemisphere because it is in the region of the Coma Berenices at a distance of 31 million light-years. This color image shows the disk bulging of the galaxy and its central heart dominated by the lights of a population of yellow stars. The heart is obscured by clouds of dust remarkably cut the central galactic nucleus. This large island Universe similar to our Galaxy has a diameter of 100 000 light-years. Some consider NGC 4565 as a masterpiece in heaven.

Image: The spiral galaxy NGC 4565 order by the slice, in the region of the Coma Berenices. We note the important band of dust that hides part of the bulb. It belongs to the cluster of the Virgin. Shot from Earth, it presents its disk of gas and dust profile. It took 2h30 posed for this picture with the Ritchey-Chrétien telescope of 32 centimeters. Robert Gendler, Connecticut, CCD.

Galaxy NGC3370

The spiral galaxy NGC 3370 is located about 100 million light-years from Earth in the direction of the constellation Leo. It closely resembles our own Milky Way, by its shape and size. In this beautiful image can be seen far into the orange color of many other galaxies scattered across deep space. The data collected from the image sufficiently precise, were used to determine precisely the distance to this galaxy by studying individual stars such as Cepheids. NGC 3370, in 1994 the spiral galaxy hosted a stellar explosion strong studied at the time.

Galaxy NGC7331

NGC 7331, with a diameter of 100 000 al, is the main galaxy of a group of galaxies known as Deer Lick group in the constellation of the northern hemisphere, Pegasus. This group is not a mass as small galaxies visible on the image here against are much more remote than NGC 7331. The heart of the galaxy is composed of old stars that give reddish brown this aspect. As against its spiral arms are home to more young stars, which give them the color blue. It is about 46 million light-years from Earth in the constellation Pegasus Boreal. In a same size as our Milky Way galaxy, NGC 7331 is often seen as the apparent collection of galaxies that we see in the background, like a galactic clusters.But they are not in the same cluster because they are located too far (several hundred million light years) of the galaxy NGC 7331.

The image of the universe Islands, an impressive depth of field, was obtained from data collected at the Calar Alto Observatory in southern Spain. NGC 7331 offers us here, the characteristic richness of its environment.

Galaxy NGC 918

The spiral galaxy NGC 918 is at the center of this beautiful celestial landscape.The galaxy is about 50 000 light years in diameter and is about 60 million light years from us in the constellation Aries.In the foreground of the picture you see the glistening stars in our galaxy, the Milky Way, they are bathed in clouds of cosmic dust reflecting weak starlight.Beyond its beauty, astrophysicists see this particular image, the light of a supernova, SN 2009js, they had no image.Pictured is the supernova to the marked locatiosn of the 2 strokes, just below and left of the center of the galaxy. This supernova is the explosion of a massive star in the plane of NGC 918.

It has been observed for the first time in October 2009 by teams from Japan and the United States specializing in the research of a supernova.

Image: The galaxy NGC 918, a beautiful spiral galaxy in the center of the image.Credit & Copyright: Joseph Brimacombe

Polar ring galaxy NGC 660

The spiral galaxy NGC 660 polar ring is the center of a galaxy in the constellation Pisces. NGC 660 is a distance of more than 20 million light years from our solar system. Particularly rare form earned him the title of polar ring galaxy. It may be noted in this photo, a rotating ring, nearly perpendicular to the plane of the galaxy, as if the ring came from another galaxy captured. The polar ring of NGC 660 has a diameter of about 40 000 light years, it is larger than the disk of the galaxy.The few polar ring galaxies are of particular interest to scientists studying the gravitational influence of dark matter on the rotation of the disk and the polar ring.

Image: Located 20 million light years from our solar system, the galaxy NGC 660, polar ring, seems to have been formed from the collision of two galaxies. Credit & Copyright: Immo Gerber & Dietmar Hager (TAO)

Galaxy M88 or NGC 4501

The French astronomer Charles Messier described the 88th entry in his famous catalog as a "spiral nebula without stars." Advances in instrumentation allow us to know that M88 is indeed a beautiful spiral galaxy, but full of stars, gas and dust, just like our own Milky Way. Indeed, M88 is even one of the brightest galaxies in the Virgo cluster, about 50 million light-years from us. The magnificent spiral arms of M88 are easily distinguished on this cosmic portrait colorful, with their veins begin dust around the nucleus and enhanced the blue young star clusters and pink regions of star formation. The yellow cast of the nucleus is due to its relatively old population of stars.

The spiral galaxy M88 has a diameter in excess of 100 000 light years, it is located in the constellation Coma Berenices. Its magnitude remains fairly low: 9.6 in magnitude.

Barred spiral galaxy NGC 891

NGC 891 galaxy is a barred spiral galaxy about 30 million light-years away in the constellation Andromeda. It was discovered by William Herschel October 6, 1784. This galaxy is a member of the NGC 1023 galaxies in the local supercluster. The object is visible in small telescopes of moderate size, as an elongated patch of faint light spread over a band of dust. This spiral galaxy extends about 100,000 light years in diameter and is distant about 30 million light years from our galaxy in the constellation Andromeda. NGC 891 is very similar to our own galaxy, the Milky Way. Like all spiral galaxies, it has a thin and flat galactic disk and a central bulge in the middle. In this picture we can see detail of thick veins of dust. A distinction is also on the presentation by the edge of NGC 891 filament of dust that extend for hundreds of light years above and below the disk. These dusts were likely ejected from the disk by supernova explosions or intense activity of star formation.

Small companion galaxies are also visible near the galactic disk.

Image: The barred spiral galaxy NGC 891Credit: NASA, STScI, WikiSky

Spiral galaxy M51, or NGC 5194

The spiral nebula, M51 is a large galaxy as it is over 60,000 light years in diameter. This is a pair of galaxies, distant 31 million light-years. Featuring a clear spiral structure and also cataloged as NGC 5194, M51 is a member of a well known duo of interacting galaxies, spiral arms sweeping the companion galaxy NGC 5195. This composite image combines contrasts dramatically enhanced images of M51 obtained with the 1.2-m telescope of Calar Alto Observatory. The data include long exposures through a hydrogen-alpha filter that focuses on emissions of atomic hydrogen. The hydrogen emission regions in the typical reddish color are called HII regions, regions where star formation is intense and located mainly along the spiral arms of M51. This composite image also shows areas of hydrogen emission in the weak structures extending beyond NGC 5195, near upper of the image.

The Whirlpool Galaxy or NGC 5194 Tourbillon 60 000 light years in diameter is also known as the M51. It absorbs by NGC 5195, his companion at the top.

Tadpole galaxy or Arp 188

What is the explanation of the long tail of the Tadpole galaxy? This image recorded by the camera of the Hubble Space Telescope, we see distant galaxies in the background of the spiral galaxy Arp 188. The Tadpole Galaxy is less than 420 million light-years away toward the northern constellation Draco. Its tail is about 280,000 light years in length and contains massive blue star clusters. It seems that a galaxy Arp 188 has crossed the Tadpole and stretched by gravitational attraction. This meeting would have torn the stars, gas and dust in the spiral galaxy, forming the spectacular tail. Like the tadpole, the Tadpole Galaxy is expected to lose its tail as it ages, the clusters of stars forming the tail when smaller satellites of this large spiral galaxy.

Galaxy NGC 6872 and IC 4970

The galaxy NGC 6872 is a massive spiral galaxy at least 4 times larger than our Milky Way high. It is over 400,000 light years in diameter and is located about 200 million light-years away in the constellation of the Peacock. His arms are stretched by gravitational interactions, it has with the small neighboring galaxy, the galaxy IC 4970. NGC 6872 and IC 4970 are two interacting galaxies located 300 million light-years. On the picture against this small galaxy is on the right just below NGC 6872. Note also a fracture of the arm galaxy NGC 6872 seems attracted by the gravitational pull of IC 4970. This beautiful image was taken by the telescope of 8 feet in diameter Gemini South in Chile. The Gemini Observatory is an astronomical observatory consisting of two 8-meter telescopes, one for each hemisphere of the Earth. The telescopes were funded by a consortium of institutions of the United States, the United Kingdom, Canada, Brazil, Argentina, Chile and Australia.

Image: NGC 6872 and IC 4970 are two interacting galaxies located 300 million light-years. NGC 6872 is a barred spiral galaxy (SBb) very large, and magnitude 11.6. IC 4970, smaller, is of type S0. Its gravitational interaction of the galactic arms of NGC 6872 can explain the broken form of the right.Credit: Sydney Girls High School Astronomy Club, Travis Rector (Univ. Alaska), Ángel López-Sánchez (Australian Astronomical Obs./ Macquarie Univ.), Australian Gemini Office

Sleeping Beauty galaxy of M64

Messier 64 is the famous spiral galaxy also known as the Black Eye Galaxy of Sleeping Beauty. The structure of dark dust hiding millions of stars located behind. Observations have shown that the gas regions outside of this spiral galaxy rotates in the opposite direction relative to the stars. The inner part of about 3000 light years in radius, rubs along the outer edge of the disc, which rotates in the opposite direction and extends to 40 000 light years, at a speed of 300 km/s . Collisions between the gas inside and outside regions generate many hot blue stars and the nebulae show pink. The image was taken by the Hubble Space Telescope in 2001 and was published in 2004. The fascinating internal motions of M64, also referenced as NGC 4826, are interpreted as the result of a collision between a small and a large galaxy, the resulting mixture is not yet stabilized.